Saturday 12 May 2007 18.45 EDT
First published on Saturday 12 May 2007 18.45 EDT

Moral Minds: How Nature Designed Our Universal Sense of Right and Wrong

by Marc D Hauser

512pp, Little, Brown, £25

According to Marc Hauser, "morality is grounded in our biology". We've heard this sort of thing before, of course - from evolutionary biologists, for instance, who claim that natural selection favours altruistic behaviour, since acting benevolently towards other people is a way of securing our genetic posterity. Some proponents of the evolutionary explanation go further, and infer from this that what seem to be our moral concerns aren't our real concerns at all, and that what looks like altruism is in fact just a disguise for the operation of selfish genes.

Though Hauser himself believes that the moral machinery of human brains has been designed by the "blind hand" of Darwinian selection, he rejects such extreme interpretations. There's no gene for altruism, he says, so we can't derive specific rules for conduct from the structure of our DNA. And for that reason, we shouldn't worry that our genetic inheritance leaves us trapped in an unchanging set of moral beliefs or judgments. On the contrary, our biology does not fix the range of possible moral systems, which is constrained only by history and culture. What that biology gives us is a set of very general principles on the basis of which we are able to develop one system of moral beliefs or another.

These general principles are at the heart of Hauser's argument in Moral Minds. His contention, which he thinks amounts to nothing less than a "radical rethinking" of the nature of morality, is that human beings are creatures born with innate "moral instincts". Because Homo sapiens is the only species to construct complex moral systems, morality has to be grounded in some distinctive property of the human brain - what Hauser calls a "moral organ" or "moral grammar".

As the latter description suggests, Hauser's inspiration here is the work done in theoretical linguistics by Noam Chomsky. Chomsky argues that the ability of children to learn to talk, which involves mastering highly complex rules of grammar, couldn't simply be acquired by listening to competent adult speakers. There must be an innate "universal grammar" underlying different languages, deep structures that can be uncovered through painstaking comparative study.

Hauser builds on the "linguistic analogy" suggested by the philosopher John Rawls, who thought that a satisfactory account of our moral capacities would involve appealing to intuitive principles that we aren't necessarily capable of articulating for ourselves. Just as we generate different, and mutually unintelligible, languages on the basis of universal grammatical principles, so, Hauser argues, there are deep moral "intuitions" that underlie cultural variations in social norms.

In order to uncover this "universal moral grammar", Hauser devised a "moral sense test". The test presented subjects with a number of so-called "trolley" problems, imaginary dilemmas dreamt up by philosophers and designed to tease out people's moral intuitions. Imagine, for example, that you're standing on a footbridge from which you can see a driverless tram hurtling in the direction of five people stranded on the track. The only way of stopping the tram and saving the lives of those people is to drop a heavy weight in its path. As it happens, a fat man is also standing on the bridge. Should you push the fat man to his death in order to stop the tram or leave him unmolested, in which case those on the track will die?

Hauser reports that only 10% of respondents said it was morally permissible to push the fat man from the bridge. From this and similar results, he deduces a universal "intention principle", according to which intended harm is morally worse than harm that is foreseen but not directly intended. What is unclear, however, is why Hauser thinks data like these also license claims about the existence of a discrete moral faculty or "organ". It is one thing to articulate principles that help to make sense of our intuitive responses to moral dilemmas, but quite another to conclude from this that such principles must belong to a particular region of the brain.

Moral Minds is full of fascinating reports on psychological experiments, few of which offer any obvious support for Hauser's ambitious claims about moral grammar. This accounts, in part, for the book's longueurs - that and the fact that Hauser's rather colourless prose style is no match for that of scientific popularisers such as Steven Pinker or Richard Dawkins.

Hauser's extravagant promise, in the prologue, to "explain how an unconscious and universal grammar underlies our judgments of right and wrong" is therefore not fulfilled. In fact, he comes close to acknowledging this in a somewhat deflating conclusion when he concedes that the "science of morality" is still in its infancy. And there is nothing here to suggest that this nascent discipline will conquer the "proprietary province of the humanities" any time soon.